The arrangement relates to a method for producing a cooling duct piston and to a cooling duct piston for an internal combustion engine.
Cooling duct pistons for internal combustion engines are known in principle in the prior art. Such pistons have a peripheral cooling duct located radially behind the ring belt in which a medium, such as engine oil, circulates. This cooling medium is introduced, for example, injected, into the cooling duct through at least one inlet opening, The cooling medium then circulates in the cooling duct to dissipate the heat in the piston crown and exits again through at least one outlet opening. An additional cooling space is located inside the cooling duct around the piston axis, often below the combustion bowl. A cooling duct piston of this type is known, for example, from DE 10 2007 018 932 A1.
In the case of this known cooling duct piston, a piston upper part and a piston lower part are initially produced so that these two parts can be produced, i.e. formed, optimally with respect to their design characteristics and also from the aspect of process operations. Following production of the two parts, the two parts are joined, for example, using friction welding.
It is known in the prior art that the cooling duct piston from DE 10 2007 018 932 A1 has an outer, peripheral annular cooling duct and, approximately below a combustion bowl, a dome-shaped cooling space. Using this design, it is possible, for example, for a cooling medium to be injected from an injection nozzle through an inlet opening into the outer annular radial cooling duct, where it circulates and reaches the internal cooling space through at least one, or several, overflow passages. From there, the cooling medium can leave the central cooling space through a central bore through which the piston stroke axis runs to dissipate the heat in the piston crown (i.e., the area behind the ring belt). Naturally, it is also possible for the flow to circulate in the opposite direction.
It is necessary to introduce the at least one overflow bore starting from the inner cooling space in the direction of the outer cooling duct before the two parts are produced. To do this, it is necessary to design the contour of the inner cooling duct (or cooling space) with a constant wall thickness towards the combustion bowl. Thus, it was possible to introduce these bores at any angle to the axis of the overflow bore by first countersinking the material at the point where the bore is to be introduced using a cutting bit and then boring the overflow bore after changing tools. This production step is costly, however, because two tools have to be used so that two successive production steps and/or a tool change are/is required, which is disadvantageous in the series production of such cooling duct pistons. Countersinking the material in the area in which the overflow bore is to be introduced is necessary because, in the prior art (FIG. 2 from DE 10 2007 018 932 A1), the axis of the overflow bore is not aligned at a right angle to the corresponding wall of the cooling space.
It would be desirable to improve a production method for overflow bores in cooling duct pistons, in particular, with respect to reduced production costs.